A conventional optical binocular has a pair of monocular telescopes which are coupled together by a supporting frame, the frame commonly including a center hinge to enable adjustment of the interpupillary spacing of ocular or eyepiece lenses of the telescopes. In conventional instruments of this type, sharp focus of the image of an object being viewed is achieved by rotating individual focus rings on the two eyepieces, or by rotating a center-focus wheel which is coupled to both telescopes.
Several embodiments of an important advance in binocular design are shown in U.S. Pat. Nos. 3,540,792 and 4,066,329, the disclosures of which are incorporated herein by reference. These improved designs provide a short-stroke focus knob which permits simple and rapid focusing of the image. As explained in detail in the aforementioned patents, a fast-focus mechanism enables more accurate focus adjustment, and has been found to provide a natural and comfortable way for binocular users to achieve optimum viewing of objects at varying ranges.
In U.S. Pat. No. 4,066,329, there is disclosed a center-focus binocular having a short-stroke treadle or seesaw knob which is mounted to be rotatable about an axis which is generally parallel to the optical axes of the telescopes. The improved knob herein disclosed is similar in many respects to the aforementioned knob, but the new knob is mounted to rotate about an axis which is perpendicular rather than parallel to the telescope optical axes. The new arrangement has been found to be especially suitable for relatively small binoculars which may be held in only one hand, and the knob is easily actuated in rocker fashion by two fingertips while the object of interest is being viewed.